1. Field of the Disclosure
The present invention relates to methods for reducing the friction resulting from turbulent and transitional flow in saline aqueous fluids.
2. Background of the Related Art
In a well stimulation operation, a large amount of fracturing fluid is pumped down a well bore hole under high pressure and at high flow rates to a depth ranging from about 500 meters to 6 kilometers or more, causing the rock formation surrounding the well bore to fracture. The pressure is then relieved allowing the oil to seep through the fractures into the well bore where the oil is pumped out of the well bore to the surface.
The turbulence produced as the fracturing fluid is pumped through the pipe under pressure results in the production of friction, thereby increasing the amount of energy required to move the amount of fluid at the same speed. In applications such as coiled tubing drilling (CTD) a hydraulicly powered device sometimes referred to as a “mud motor” is fixed to the end of a long, narrow section of coiled tubing (CT). When a fluid is pumped at high velocity through coiled tubing that has been deployed appropriately in an oil well, the fluid flow causes the “mud motor” to turn a drill bit at high rates of rotation and to excavate material encountered in the path of the drill bit. The material excavated by the drill bit may be subterranean rock at the bottom of the well or a temporary plug that has been emplaced in a well at or toward the “toe” of the well and in front of a hydraulicly fractured zone so that an additional hydraulicly fractured zone can be emplaced at a location at or somewhat more toward the “heel” of the well. Unfortunately, when the fracturing fluid is pumped at high velocity through the coiled tubing, the pressure of the fluid being pumped into the coiled tubing may rise to unacceptable values, stressing the coiled tubing to its mechanical limit and reducing its lifetime for subsequent reuse in similar operations. Therefore, it is desirable to reduce the hydrodynamic drag or hydrodynamic friction in the coiled tubing by injecting a drag or friction reducing material into the fracturing fluid.
Generally, high molecular weight linear polymers, referred to as friction reducers, are used to alter the rheological properties of a fluid so that the turbulent flow is minimized, thereby reducing energy loss in the fluid as it is pumped through the pipe. A good friction reducer will cause a fluid to experience a large decrease in friction at small concentrations within the fluid, and will have a high level of shear stability, temperature stability, and pressure stability.
Standard latex polymers may be made with suitable molecular weights for use as friction reducers, but such standard latex emulsion polymers are solids that must be dispersed in a hydrocarbon solvent and stabilized with surfactants. However, these standard latex polymers are of limited utility as friction reducers due to the environmental unfriendliness of the hydrocarbon solvent and surfactants, for example in the case of spill or discharge on land or on an off shore platform. The latex polymers also must be inverted prior to use, which involves the use of additional surfactants.